import java.security.KeyPair;

import java.security.KeyPairGenerator;

import java.security.PrivateKey;

import java.security.PublicKey;

import java.security.SecureRandom;

import java.security.Security;

import java.security.Signature;

public class SignatureSignAndVerify {

      public static void main(String args[]) throws Exception {

        Security.addProvider(new org.bouncycastle.jce.provider.BouncyCastleProvider());

        KeyPair keyPair = generateKeyPair();

        byte[] data = { , , , , , , , , ,  };

        byte[] digitalSignature = signData(data, keyPair.getPrivate());

        boolean verified;

        verified = verifySig(data, keyPair.getPublic(), digitalSignature);

        System.out.println(verified) ;

        keyPair = generateKeyPair();

        verified = verifySig(data, keyPair.getPublic(), digitalSignature);

        System.out.println(verified);

      }

      public static byte[] signData(byte[] data, PrivateKey key) throws Exception {

        Signature signer = Signature.getInstance("SHA1withDSA");

        signer.initSign(key);

        signer.update(data);

        return (signer.sign());

      }

      public static boolean verifySig(byte[] data, PublicKey key, byte[] sig) throws Exception {

        Signature signer = Signature.getInstance("SHA1withDSA");

        signer.initVerify(key);

        signer.update(data);

        return (signer.verify(sig));

      }

      public static KeyPair generateKeyPair(long seed) throws Exception {

        Security.addProvider(new org.bouncycastle.jce.provider.BouncyCastleProvider());

        KeyPairGenerator keyGenerator = KeyPairGenerator.getInstance("DSA");

        SecureRandom rng = SecureRandom.getInstance("SHA1PRNG", "SUN");

        rng.setSeed(seed);

        keyGenerator.initialize(, rng);

        return (keyGenerator.generateKeyPair());

      }

}